1. Field of the Invention
The present invention relates to a wheel motor device which has a hydraulic motor main body forming an HST in cooperation with a hydraulic pump main body that is operatively driven by a drive source and which is placed separately from the hydraulic pump main body such that it can be positioned close to a corresponding driving wheel.
2. Related Art
There has been conventionally known a wheel motor device which has a hydraulic motor main body forming an HST in cooperation with a hydraulic pump main body that is operatively driven by a drive source and which is placed separately from the hydraulic pump main body such that it can be positioned close to a corresponding driving wheel (see, for example, Japanese Unexamined Patent Publication No. 2006-096112, Japanese Unexamined Patent Publication No. 2005-195070, and Japanese Unexamined Patent Publication No. 2005-028914, which are hereinafter referred to as prior document 1 to 3, respectively).
The wheel motor device can be preferably used in a working vehicle such as a mid-mount mower tractor which is required to ensure a free space between a pair of driving wheels usable as an installation space for a rear discharge duct and the like.
More specifically, the wheel motor devices described in the prior documents 1 to 3 include a speed-reduction gear mechanism for reducing a speed of the rotational power output from the hydraulic motor main body, an output member for outputting the rotational power whose rotational speed has been reduced by the speed-reduction gear mechanism to the corresponding driving wheel, and a brake mechanism capable of operatively and selectively applying a braking force to the output member, in addition to the hydraulic motor main body fluidly connected to the hydraulic pump main body.
Since the conventional wheel motor devices include the speed-reduction gear mechanism, it is possible to employ a high-rotation/low-torque type hydraulic motor main body as the hydraulic motor main body. This can reduce the size of the hydraulic motor main body and also can reduce the leak of the hydraulic fluid from the hydraulic motor main body, thereby enhancing power transmission efficiency of the HST.
Meanwhile, it is desirable to reduce the size of the wheel motor device including the above-described components with respect to the direction of the rotational axis line of the corresponding driving wheel (namely, in the widthwise direction of the working vehicle).
Namely, by reducing the size of the wheel motor device in the direction of the rotational axis line, it is possible to ensure the free space between the pair of driving wheels as much as possible.
Further, the wheel motor device is desired to reduce the size of the brake mechanism as much as possible, while increasing the degree of freedom in designing the brake mechanism.
However, there exists no wheel motor device capable of attaining the above-described two requirements at the same time.
Specifically, the wheel motor device described in the prior document 1 includes a motor shaft positioned inwards in the vehicle widthwise direction than the corresponding driving wheel with being parallel to the rotational axis line of the corresponding driving wheel, a hydraulic motor main body supported on the motor shaft in a relatively non-rotatable manner, a speed-reduction gear mechanism operatively connected to an outer end portion of the motor shaft in the vehicle-widthwise direction (the end portion on as side close to the driving wheel), an output member for outputting the rotational power inputted from the speed-reduction gear mechanism to the driving wheel, and a brake mechanism positioned inwards in the vehicle-widthwise direction than the hydraulic motor main body in such a way as to selectively apply a braking force to an inner end portion of the motor shaft in the vehicle-widthwise direction (the end portion on a side away from the driving wheel).
Since the wheel motor device described in the prior document 1 is configured so that the brake mechanism applies the braking force to the motor shaft which is positioned on an upstream side in a power transmission direction than the speed-reduction gear mechanism, it is possible to achieve a reduction of the brake capacity required for the brake mechanism, thereby reducing the size of the brake mechanism.
However, the brake mechanism is positioned inwards in the vehicle-widthwise direction than the hydraulic motor main body, thereby inducing the problem that the free space between the pair of driving wheels is reduced due to the presence of the brake mechanism.
The wheel motor device described in the prior document 2 includes a motor shaft placed positioned inwards in the vehicle-widthwise direction than the corresponding driving wheel with being parallel to the rotational axis line of the corresponding driving wheel, a hydraulic motor main body supported on the motor shaft in a relatively non-rotatable manner, a speed-reduction gear mechanism operatively connected to an outer end of the motor shaft in the vehicle-widthwise direction, an output member for outputting the rotational power inputted from the speed-reduction gear mechanism to the driving wheel, and a brake mechanism inserted between the speed-reduction gear mechanism and the outer end of the motor shaft in the vehicle-widthwise direction, in the direction of the rotational axis line (in the vehicle-widthwise direction) in such a way as to selectively and operatively apply a braking force to the output member.
Since the wheel motor device described in the prior document 2, similarly to the wheel motor device described in the prior document 1, is configured so that the brake mechanism applies the braking force to the motor shaft which is positioned on an upstream side in a power transmission direction than the speed-reduction gear mechanism, it is possible to achieve a reduction of the brake mechanism in size.
However, the brake mechanism is positioned between the motor shaft and the speed-reduction gear mechanism with respect to the vehicle-widthwise direction, thereby inducing the problem that the free space between the pair of driving wheels is reduced due to the presence of the brake mechanism.
The wheel motor device described in the prior document 3 includes a motor shaft positioned inwards in the vehicle-widthwise direction than the corresponding driving wheel with being parallel to the rotational axis line of the corresponding driving wheel, a hydraulic motor main body supported on the motor shaft in a relatively non-rotatable manner, a speed-reduction gear mechanism operatively connected to an outer end of the motor shaft in the vehicle-widthwise direction, an output member for outputting the rotational power inputted from the speed-reduction gear mechanism to the driving wheel, and a brake mechanism configured so as to selectively apply a braking force to an intermediate shaft in the speed-reduction gear mechanism.
More specifically, the speed-reduction gear mechanism includes the intermediate shaft which is placed at a position displaced from both the motor shaft and the output member with being parallel to both the shafts, a first speed-reduction gear train for performing primary speed-reduction between the motor shaft and the intermediate shaft, and a second speed-reduction gear train for performing secondary speed-reduction between the intermediate shaft and the output member.
Further, the brake mechanism is positioned so as to selectively and operatively apply the braking force to the outer end portion of the intermediate shaft in the vehicle-widthwise direction (the end portion on a side away from the driving wheel).
Since the motor wheel device described in the prior document 3, the brake mechanism is configured so as to apply the braking force to the intermediate shaft displaced from the motor shaft, it is possible to prevent the wheel motor device from being lengthened in the vehicle-widthwise direction (in the direction of the axis line of the motor shaft) due to the provision of the brake mechanism, thereby preventing the occurrence of the problem that the free space between the pair of driving wheels is reduced due to the presence of the brake mechanism.
However, in the wheel motor device described in the prior document 3, the position at which the brake mechanism is placed depends on the position of the intermediate shaft in the speed-reduction gear mechanism, thereby degrading the degree of freedom in designing the brake mechanism.
Further, in the prior document 3, the speed-reduction gear mechanism applies the braking force to the intermediate shaft which is rotated at a rotational speed which has been reduced from the rotational speed of the motor shaft by the first speed-reduction gear train.
This structure induces the problem that the brake capacity of the brake mechanism cannot be sufficiently reduced.